1. Field of the Invention
The present invention relates generally to apparatus for positioning objects, and more particularly, but not exclusively, to techniques for characterizing the performance of such apparatus including those employed in the manufacture of integrated circuits.
2. Description of the Background Art
An object positioning apparatus may include a support member for supporting an object and a motion mechanism for moving the support member. To accurately position an object, the motion mechanism may include sensors that are coupled to a motion controller. The motion controller may read the sensors to get information relating to the support member, such as its current location, velocity, acceleration, and like information. For example, a motor driving the support member may include an encoder that is coupled to the motion controller. From the output signal of the encoder, the motion controller may determine how far the motor has driven the support member. Besides those related to motion, other factors that may affect accurate positioning of an object may also be monitored. For example, sensors for monitoring pressure, air flow, temperature, and other conditions may be coupled to a controller for data acquisition and control purposes.
In the manufacture of integrated circuits, for example, object positioning apparatus are employed to accurately position semiconductor wafers. Examples of such apparatus include those employed in photolithography tools. Generally speaking, a photolithography tool is a system for forming a pattern on a wafer. A photolithography tool typically includes an apparatus for positioning a wafer referred to as a xe2x80x9cwafer stagexe2x80x9d, and an apparatus for positioning a mask referred to as a xe2x80x9cmask stagexe2x80x9d. The mask has a pattern to be transferred on the wafer. The wafer is positioned under the mask, which is under a light source. By shining a light beam of suitable wavelength through the mask, the mask pattern is imprinted on a photosensitive material on the wafer.
Because of the precision involved in the manufacture of integrated circuits, photolithography tools employ accurate wafer and mask stages. As integrated circuits become more complex, the need for more accurate stages becomes greater. Thus, when a wafer or mask stage is incapable of accurate movement, the photolithography tool is taken xe2x80x9cdownxe2x80x9d for troubleshooting. For example, a photolithography tool is taken down when unwanted vibrations on a wafer stage prevent accurate alignment of a wafer relative to a mask. Unfortunately, traditional techniques for troubleshooting positioning related problems take a relatively long time and are difficult to perform. One such troubleshooting technique involves turning off a component of the photolithography tool that may be generating too much vibration, running a pass/fail test and, if the test fails, turning off another component and re-running the pass/fail test. The just mentioned steps are performed until the source of the vibration is identified and repaired. Thus, if the photolithography tool has a lot of components or if the vibration is coming from more than one component, it will take some time before the photolithography tool can be brought back up to operational condition.
In one embodiment, an object positioning apparatus is characterized by receiving sensor data from a sensor, processing the sensor data to compensate for sensor drift, and analyzing the resulting processed sensor data to determine a characteristic of the apparatus. Compensating for sensor drift cleans up the sensor data so that they may be properly analyzed and compared against known good sensor data, for example. Compared to conventional techniques, the present invention allows for more efficient troubleshooting of object positioning apparatus.